Method and apparatus for controlling refrigerating machines



Oct. 25, 1938. LB. M. BUCHANAN 2,133,966

MEHOD AND APPARATUS FOR COITROLLING REFRIGERATING MACHNES Filed Aug. 18, 1957 2 Sheets-Sheet [25g LESLIE BM. BucHnNnN.

BY A .I A

ATTORNY Oct. 25, 1938.. Y L. B. BUc'H'AN-AN 2,133,966

METHOD AND APPARATUS FOR CONTROLLING REFR-L'GEIRATING MACHINES Filed Aug. 18, 1937 2 Sheets-s118612 f, v FIGL. 3.

WITNEssEs: INVENTOR LESLIE B` M. Bucnnmm @ww BY I UNITED STATES PATENT oFFlcEj METHOD AND APPARATUS Fon CONTROL- LING REFRIGERATmG MACHINES Leslie B'. M. Buchanan, Springfield, Mass., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application August 18, 1937, Serial No. 159,657

14 Claims.

My invention relates to refrigerating machines and it has for an object to provide an improved method and apparatus for controlling the same.

A further object of the invention is to provide an improved method and apparatus for controlling the operation of a refrigerating machine in response to temperature conditions in different zones being cooled.

A further object of the invention is to provide an improved control for a two-temperature refrigerator that will be inexpensive to construct.

A still further object of the invention is to provide an improved control for a refrigerating machine vthat is responsive to the temperatures of its cooling element and the media cooled by the same. These and other' objects are effected by my invention as will be apparent from the following description and claims, taken in connection with the accompanying drawings, forming a part of y this application, in which:

Fig. 1 is a diagrammatic view of a two` temperature refrigerator controlled in accordance with my invention; l

Fig. 2 shows-a second form of two temperature refrigerator having my improved control applied thereto; and

Fig. 3 is a diagrammatic view of a refrigerating system employing a single evaporator and controlled in accordance .with my invention.

.Descriptio'w-Fig. 1 l Reference will now be had to 1 of the drawings wherein the numeral I0 generally indi cates a cabinet structure that defines relatively high and low temperature zones or chambers II and I2 for the storage of perishables. High and low temperature evaporators I3 and I4 of suitable construction are disposed within the zones for refrigerating the same and are supplied with condensed refrigerant by a condensing unit, generally shown at I5, and including a compressor IS, drivenby an electric motor I1, and a condenser I8. The latter is cooled in any well known manner, such as, for example, by a fan I9.

The refrigerat-ing system which I have chosen to show has the evaporators I3 and I4 connected in series 'for the iiow of refrigerant, the higher temperature evaporator I3 receiving condensed refrigerant from the condenser I8 through a conduit 2| and the refrigerant vaporized in both evaporators being returned to the compressor I6 through'a 'suction conduit22. A suitable expension device, such as a high side float valve 23 may be connected in the conduit 2I for reduc- (Cl. 62-4) ing the pressure of the condensed refrigerant to the value maintained in the evaporator I3 by the compressor I6. In order that the evaporators are operated at different pressures and temperatures,`

a restricting device, such as, for example, a capillary tube 24 is interposed between the evaporators drawn by the compressorl from the evaporator I I4 and is compressed toa relatively high pressure. The high pressure vapor is conveyed by a conduit 25 to the condenser I8 wherein it is cooled and condensed.- Liquid refrigerant is conveyed through the conduit 2| to the evaporator I3, the valve 23 reducing the pressure of the liquid'to the pressure of Vaporization in the condenser I3. A portion of the liquid is vaporized in the evaporator I3 and the remaining liquid and the gaseous refrigerant pass through the restricting device 24 to the low temperature evaporator I4. Vaporization of the liquid refrigerant is completed in the low temperature evaporator I4 at low pressure and temperature. The difference in temperatures of the two evaporators is obtained by the restricting device 24 which effects a suitable difference in vaporizing pressures.

Heretofore, it has been the practice to control the circulation of refrigerant in. a two temperature refrigerator in accordance with temperature conditions in one or the other of the refrigerated zonesl or'to provide separate thermostats which respond to the temperatures in their respective zones for this purpose. When the control is responsive to the temperature of a single zone for effecting its control, the temperature of the other zone will vary substantially, depending upon the heat load thereon. When controlling the circulation of refrigerant from both zones by separate thermostats, th e control mechanism is necessarily expensive.y

In accordance with my invention, I propose to use a single thermostatshown generally at 25, and including an expansible bellows 26. The

latter is connected to and communicates with a tube 21 having portions shown by way of example as a pair of bulbs 28 and 29. The bulbs 28 `and 29 are disposed in heat transfer relation with the respective'evaporators I3 and I4 and dene con- -ture bulb. The lower temperature bulb contains the liquid becauseits temperature determines the` pressure of vaporization of the iluid and any tendency to increase this pressure due to vaporization of liquid which may be present in the other higher temperature bulb is precluded by the condensation of such vaporized fluid in the lower temperature bulb. It will be apparent from the foregoing description that as the temperature of one bulb is reduced vbelow the temperature oi' the other, the iiuld in the other vaporlzes and condenses in the bulb whose temperature has 'been depressed. Therefore, the liquid always collects in the lower temperature bulb and its pressure of vaporlzation is determined' by the temperature of this bulb.

As the bulb 29 is subjected to the lower tem'- perature evaporator Il, it normally determines the pressure in the bellows 28 and, therefore, controls the operation of the thermostat 25. In accordance with my invention, the thermostat is under control of the bulb 29 during inactive periods of the compressor I6 and therefore determines the temperature at which operation of the compressor I 5 is initiated. During operation of the compressor I6, I transfer control to the bulb 28 which determines the temperature at which the compressor I6 is stopped. This transfer of control is accomplished by heating the bulb 29 to a temperature in excess of the temperature of the bulb 28. Heating of the bulb 29 may be effected in any suitable manner but, as shown, I

' employ the relatively warm high pressure refrig erant passing from the condenser I8 to the expansion device 23 for this purpose. Accordingly, a portion ofthe conduit 2l is disposed in heat transfer relation with thebulb 29 and a portion of the evaporator I4 as shown at 35.

Operation-Fig. 1

As shown in the drawings (Fig. 1) the thermostat switch 32 is open and the compressor motor I1 is inactive, the temperature of the bulb 29 being below the value at which the switch 32 is closed. The flow of condensed refrigerant in the conduit 2| is substantially stopped so that 'the bulb 29 is cooled by the low temperature evaporator I4 to a temperature below that of the bulb 28 and, therefore, the bulb 29 controls operation of the thermostat 25.

When the temperature of and its bulb 29 rises to a predetermined value, for example, 25 F., the switch 82 is closed for energizing themotor I1 and initiating operation of the compressor I8. 'l'.'he temperature of the high temperature evaporator `I3 at this time is relatively high, for example, 35 F. Circulation of refrigerant through the evaporators is initiated and, as described heretofore, vaporlzation is effected in the respective evaporators at different temperatures and pressures. The flow of condensed refrigerant in the conduit 2| eiects `a rise in the temperature of the bulb 29 to a value higher than the temperature of the bulb 28. Ac-

the evaporator I8 cordingly, control of the thermostat 25 is transferred to the bulb 28 and operation of the compressor is continued until the temperature of the high temperature evaporator I3 and the bulb 28 is depressed to the desired value, for example, 23 F., at which time operation of the compressor I5 is terminated by the opening of the switch 32. At this time, the temperature of the low temperature evaporator is depressed to a relatively low value, for example', 10 F.

Control passes from the bulb 28 to the bulb 29 when the compressor I6 is stopped andpflow of heat from the condensed refrigerant to the bulb 29 is terminated, it being understood that the temperature of the bulb 29 falls below the temperature of the -bulb 28. A complete cycle of operation has now been described.

From the foregoing it will be apparent that I haveprovided an improved control wherein the circulation of refrigerant is controlled from relatively high and low temperature zonesby a single' thermostat mechanism and which may be applied to various forms of refrigerating apparatus wherein the minimum temperature of the higher temperature zone is below the maximum temperature of the low temperature zone.

Description and operation of Fig; 2

The system disclosed in Fig. 2 defines a second form of two temperature refrigerator controlled in accordance with my invention. Parts which are common to both systems shown in Figs. 1 and 2 are designated by similar reference numerals. In the present embodiment, the high and low temperature evaporators I3 and I4, respectively, are connected in free communication with each other, the pressure in both being substantially the same; A conventional pressure responsive expansion valve 4I controls admission of condensed -refrigerant to the evaporators in response to the determined value as determined by .the setting of the valve 4I, liquid refrigerant is carried into the evaporator I3 and is vaporized therein. Heat is therefore abstracted from the media in the chamber II. In'this form of refrigerating system, a conventional liquid reservoir 42 is disposed in the liquid supply conduit 2i for storing variable Y quantities o f condensed refrigerant.

The/temperature of the higher temperature evaporator I3 at which the thermostat 25 terminates operation of the compressor I6 should be somewhat higher than the temperature setting of the valve 4I so that passage of liquid to the suction conduit 22 is prevented. 'I'his adjustment ofI temperatures also assures that the bulb 29 will become colder than the bulb 28 after the com-` pressor is shut down. As the operation of the control apparatus shown in Fig. 2 is similar to the apparatus shown in Fig. 1, detailed description thereof is deemed unnecessary.

Description of Fig. 3

In this figure, I have shown my invention applied to a refrigerator structure 43 embodying a space 44 to be cooled and an evaporator 45 disposed for abstracting heat from the space 44. In this type of refrigerating system, the temperature of the space 44 at the time of terminating operation of the compressor is below the-temperature of the evaporator 45 at the time ofA initiating operation of the same. Such application may be found in commercial type refrigerators where it is desired to maintain the temperature of the air above 32 F. andto defrost the evaporator during each cycle.

A condensing unit I5 similar to the unit shown in Figs. l and 2 may be employed and its various elements are shown having similar reference numerals for parts thereof which are common to the various embodiments. Refrigerant that is condensed in the condenser I8 is conveyed to the evaporator 45 through the conduit 2I, the latter having a suitable expansion valve 46 connected therein. A portion of the conduit 2l is connected in heat transfer relation with the evaporator 45 and the bulb L. of the thermostat 25. The other bulb 28 of the thermostat is disposed in heat transfer relation with the air in the space 44. The bulb 29 is, therefore, in a relatively cool zone and the bulb 28 in a warmer zone in the space 44. The operation of the system shown in Fig. 3 will now be described.

Operation of Fig. 3

As shown, the switch 32 is open and the compressor I6 and its driving motor I'I are inactive as l the temperature of the bulb 29 is below its switch 25. As the temperature of .the evaporator 45 and the bulb 29 rises to a predetermined value, say

36 F., the switch 32 of the thermostat 25 closes and energizes the motor I'I. Operation of the compressor I6 is initiated and vaporization effected in the evaporator 45. -The flow of relatively warm liquid in the conduit 2l imparts sufcient heat to the bulb 29 to elevate its temperature above that of the bulb 28. Accordingly, the latter becomes the controlling element of the thermostat 25.

Operation ofthe compressor I6 continues until the temperature of the air adjacent the bulb 28 is depressed to a predetermined value of say 33 F., at which time the thermostat 25deenergizes the motor Il. Operation of the compressor I6 is terminated and vaporization of refrigerant in the evaporator 45 is substantially stopped. As the flow of heat to the bulb 29 from the liquid refrigerant is substantially reduced, the temperature of the bulb 29 is depressed to a value below the temperature of the bulb 28 and, therefore, again becomes the controlling element of the thermostat. At this time, the temperature of the evaporator is relatively low or at a value of say 20 F.

From the foregoing, it will be apparent that the air is maintained at a temperature above freezing at all times and that the evaporator operates part of the time at a temperature that will assure defrosting during part of the cycle.

In the various embodiments described hereto fore, I have shown a refrigerating machine of the compression type, but it is to be understood that my invention is applicable to other forms of refrigerating machines. The specic form of thermostat structure which I have shown is disclosed by way of example and it will be understood that other forms of gas type thermostats may be employed. Furthermore, I have shown bulbs 28 and 29 for containing the volatile liquid `in the thermostat but other suitable containers may be employed.

While I have shown my invention in several forms, it will be obvious to tb cse skilled in the art that it is not so limited, vbut is susceptible of various other changesand modifications without departing from the spirit thereof, and I desire,

therefore, that only such limitations shall be second thermal responsive elements disposed inheat transfer relation with said low and high temperature zones, respectively, said elements being in communication with each other and containing a volatile fluid, and means for heating said element in the low temperature zone to a temperature higher than the temperature of the element in the high temperature zone during active periods of the refrigerating machine,

whereby the element in the low temperature z one controls the refrigerating machine when it is inactive and the element in the higher temperature zone controls the machine when it is active.

3. In refrigerating apparatus, the combination rof means defining relatively low and high temperature zones to be refrigerated, evaporator means for. abstracting heat from both zones, means for circulating refrigerant through the evaporator means, a thermostat for controlling the operation of the circulating means 'and including first and second thermal responsive elements disposedl in heat transfer relation with said low and hightemperature zones, said elements being communicating and containing a volatile ,element and in a region of higher temperature, y said elements containing a volatile uid and be-4 fluid, and means for heating the thermal element i associated with the low temperature zone during periods when the circulating means isf active and to a temperature in excess of the temperature of the thermal element associated with the high temperature zone, whereby the circulating means is startedin-response to the temperature of the low temperature zone and is stopped in lresponse to the temperature of the higher temperature zone.

4. In refrigerating apparatus, the combination of means defining relatively low and higher tem- .said elements being communicating and containing a volatile fluid and means for conveying the liquid refrigerant from the condenser to .the evaporator means in heat transfer relation with the element associated with the low temperature zone.

5. The method of controlling the operation of a machine for refrigerating diierent zones of a refrigerator at different temperatures which includes initiating the refrigeration of the zones in response to a predetermined high temperature of the lower temperature zone, transferring control of the machine to the higher temperature zone during operation of the machine,

terminating operation of the machine in response to a predetermined low temperature of the higher temperature zone and returning-control of the machine to the lower temperature zone during -inactive periods of the machine.

6. In refrigerating apparatus, the combination of relatively high and low temperature evaporators, means for circulating refrigerant through the evaporators, a thermostat for controllin-g the operation of said circulating means and having first and second thermal responsive elements disposed in heat transfer relation with the high and low temperature evaporators, respectively, and means for heating the thermal responsive element associated with the low temperature evaporator during periods when the circulating means is rendered active by the thermostat.

7. In refrigerating apparatus, the combination of an evaporator structure having relatively high and low temperature portions, a compressor for circulating refrigerant through the evaporator structure, a thermostatfor controlling the operation of the compressor and having thermal responsive elements disposed in heat transfer relation with the evaporator portions, respectively, said elements containing a volatileV fluid, and means for heating the thermal responsive element associated with the low temperature evaporator portion to a temperature in excess of the temperature of the other of said thermal responsive elements during periods when the compressor is operated for the circulation' of refrigerant.

8. In refrigerating apparatus, the combination of relatively low and high temperature evaporators, a compressor for withdrawing gaseous refing it to a relatively high pressure. a condenser for condensing the compressed refrigerant. a thermostat for controlling the operation o! the compressor and including thermal responsive elements enclosing a volatile heat transfer relation with the respective evaporators and means for conveying the liquid refrigerant from the condenser to the evaporators in heat transfer relation with. the thermal re sponsive elementassociated with the low temperature evaporator.

9. In refrlgerating apparatus, the combination of means defining relatively low and high temperature zones to be refrigerated, a refrigerating the evaporators and for compress-v fiuid and disposed in machine for abstracting heat from both zones, a thermostat for initiating and terminating operation of said machine and including first and second thermal responsive elements disposed in heat transfer relation with said low and high temperature zones, respectively, and means for rendering said first and second thermal responsive elements active and inactive, respectively, during periods when the refrigerating machine is stopped and for rendering the first and second thermal responsive elements inactive and active respectively, during operating periods of the refrigerating machine.

10. In refrigerating apparatus, the combination of means defining a.zone to be cooled, an evaporatorfor cooling the media in said zone, means for condensing refrigerant vaporized in the evaporator, a thermostat for controlling the operation of the condensing means and including first and second thermal responsive elements, one of said thermal responsive elements being disposed in heat transfer relation with the evaporator and the other thermal'responsive element being disposed in heat transfer relation-with the media cooled by the evaporator, said elements being in communication with each other and containing a volatile fluid, and means for heating the element-associated with the evaporator during periods when said condensing means is active.

11. In refrigerating apparatus, the combination of means defining a zone to be cooled, an evaporator for cooling media in said zone, means for condensing refrigerant vaporized in the evaporator, a thermostatfor controlling the condensing means and including rst and second thermal responsive elements, one of said thermal responsive elements being disposed in heat transfer relation with the evaporator and the other thermal responsive element being disposed in heat transfer relation with the media cooled by the evaporator, said elements being in communication with each other and containing a volatile uid, and means for conveying the refrigerant condensed by the condensing means to the evaporator in heat transfer relation with the thermal element associated with' the evaporator.

l2. In refrigerating apparatus, the combination of a cabinet embodying a space to be cooled, an evaporator disposed for cooling the media in the s-pace, a compressor for withdrawing vaporous refrigerant from the evaporator and for compressing the same. means for condensing the compressed reirigerant, a motor for driving the compressor. a gas type thermostat for controlling energization of said motor and including first and second thermal responsive elements, one'of said thermal responsive elements being disposed in heat transfer relation with the evaporator and the other thermal responsive element being disposed in heat transfer relation with the media cooled by the evaporator, said elements being in communication with each-other and containing a volatile xlnid. and means for conveying the condensed refrigerant from the condenser to the evaporator in heat transier'relation with the elementassociated with the evaporator.

13. In reirigerating apparatus, the combination oi a cabinet defining a space to be cooled, an evaporator disposed for cooling the media in the space, a compressor vfor withdrawing vaporous refrigerant from the evaporator and for compressing the same. means for condensing the compressed refrigerant, a motor for driving the cmpressor, a switch for controlling the energization of the motor, an expansible bellows for actuating the switch and including first and second containers for a volatile uid, one of said containers being disposed in heat transfer relation vwith the evaporator and the other container being disposed in heat transfer relation with the'media cooled by the evaporator, said bellows and containers being in communication one with the other and means for conveying the condensed evaporator for cooling the media in said zone,

means for condensing refrigerant vaporized in the evaporator, a thermostat for controlling the operation of the condensing means and including rst and second thermal responsive elements, one

of said thermal responsive elements being disposed in heat transfer rel'ation with the evaporator and the other thermal responsive element being disposed in heat transfer relation with the media cooled by the evaporator, and means for rendering said rst and second thermal responsive elementsactive and inactive. respectively, during periods when the refrigerating machine is stopped and for rendering the first and second thermal responsive elements inactive and active, respectively, during operating periods of the refrlgeratlngmachine. i y

LESLIE B.. M. BUCHANAN. 

